In commercial aircraft production, conventional automatic riveting machines are utilized to attach the exterior panels of the aircraft wing to the underlying wing framework. The riveting machine typically includes three vertical spindles which extend downward rom a transfer carriage which is moved in a chordwise direction above the wing. The first spindle is typically a drill spindle which drills a hole through the wing panel and into the wing frame. The second spindle is a rivet fastener which installs the rivet and fastens the rivet within the hole. A third spindle cuts off the top of the rivet so that it is flush with the surface of the wing. During rivet installation, the transfer carriage is operated so that each spindle performs its operation sequentially and the rivets are installed in a spanwise row across the wing. Then the entire riveting assembly moves chordwise along the wing to install another spanwise row of rivets.
When installing fasteners made of materials which are dissimilar to the aircraft wing panels, such as when installing titanium fastener bolts to aluminum aircraft wing panels, it is necessary to provide a moisture barrier between the bolt and wing panel in order to prevent corrosion therebetween. This may be accomplished by automatically applying a sealant compound to the drilled hole prior to the installation of the titanium bolt. It is desirable, therefore, that this operation be performed quickly since there is a very short time span between drilling the hole and installing the fastener bolt in the hole.
There are other requirements for satisfactorily applying sealant to the bolt holes. For one, it is desirable to keep the sealant clean prior to the application of the fastener bolt. The drilling operation tends to distribute pieces of aluminum about the drill site, and can cause contamination of the sealant if it is not properly protected. Furthermore, it is important that the proper amount of sealant be applied to the hole. An insufficient amount of sealant will preclude a satisfactory barrier between the fastener bolt and the panel, whereas an excess of sealant is wasteful.
Conventional sealant applicators for automatic riveting machines have been disclosed. For example, in U.S. Pat. No. 4,144,625 by Hogenhout, and assigned to the Assignee of the present invention, there is described a sealant applicator for an automatic riveting machine whereby the applicator is vertically mounted to a drill/riveter transfer carriage which in a first operational step extends downward where the applicator tip contacts an open sealant source, and in a second operational step the applicator tip is again extended downward to deposit the sealant in a rivet hole. Another sealant applicator assigned to the Assignee of the present invention is disclosed in U.S. 3,904,718 by Kuehn, Jr., which pertains to a sealant applicator for a countersunk hole whereby the applicator tip is first cleaned and then applied with sealant by means of a movable tape in a series of independent operations.
Another sealant applicator for an automatic riveting machine is disclosed in U.S. 3,350,774 by Bridges whereby the applicator is positioned in a rivet hole between a hole forming step and a rivet applying step, in order to apply sealant to the hole.
Other conventional flow control devices have also been disclosed. For example, in U.S. 3,335,753 by Kiser, there is disclosed a control valve for a beverage dispenser whereby the control valve operates to pinch off a flexible tube in order to control fluid flow through the tube.
Another fluid dispenser control mechanism is disclosed by Kavanau in U.S. 3,390,860 whereby a fluid dispenser utilizes a flexible fluid dispensing tube which is pinched off by an arm which is spring biased to the pinched off position.
Furthermore, in U.S. 3,654,959 by Kassel, there is disclosed a proportioning control valve for metering fluid through a tube whereby the control valve includes a pair of interconnected arms having spaced apart tips which pinch a flexible tube to deliver a periodic metered flow of fluid through the tube.